Browsing by Author "Nguyen, Thanh-Hai"
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Item Open Access Penetration and microstructure of steel joints by ultrasonic-assisted gas metal arc welding(IOP Publishing, 2022-01-20) Tran-The Chung, Vinh; Nguyen, Cong Thai; Bui, Khanh Duy; Nguyen, Huu Loc; Nguyen, Van Anh; Nguyen, Thanh-Haihis work investigates the application of ultrasonic vibration to steel joints formed by gas metal arc welding. Welding is done using a metal active gas welding source with welding current of 120–160 A, 0.8-mm-diameter welding wire and 10 L/min CO2 flow. The distance from the torch to the ultrasonic horn is 120 mm. Ultrasonic vibration most affects the weld when ultrasonic vibration position is 120 mm from torch and increases the penetration when welding speed is 190 (275) mm/min for a 5-mm-thick (10-mm-thick) plate. Moreover, weld width increases when welding speed is 190 mm/min for 10-mm-thick plate. Although ultrasonic vibration does not affect the hardness of welding zones, it modifies the microstructure of the diffusion and welding-pool zones.Item Open Access Relationship among welding defects with convection and material flow dynamic considering principal forces in plasma arc welding(MDPI, 2021-09-13) Nguyen, Huu Loc; Nguyen, Van Anh; Duy, Han Le; Nguyen, Thanh-Hai; Tashiro, Shinichi; Tanaka, ManabuThe material flow dynamic and velocity distribution on the melted domain surface play a crucial role on the joint quality and formation of welding defects. In this study, authors investigated the effects of the low and high currents of plasma arc welding on the material flow and thermodynamics of molten pool and its relationship to the welding defects. The high-speed video camera (HSVC) was used to observe the convection of the melted domain and welded-joint appearance. Furthermore, to consider the Marangoni force activation, the temperature on the melted domain was measured by a thermal HSVC. The results revealed that the velocity distribution on the weld pool surface was higher than that inside the molten weld pool. Moreover, in the case of 80 A welding current, the convection speed of molten was faster than that in other cases (120 A and 160 A). The serious undercut and humping could be seen on the top surface (upper side) and unstable weld bead was visualized on the back side (bottom surface). In the case of 160 A welding current, the convection on the weld pool surface was much more complex in comparison with 80 A and 120 A cases. The excessive convex defect at the bottom side and the concave defect at the top surface were observed. In the case of 120 A welding current, two convection patterns with the main flow in the backward direction were seen. Almost no welding defect could be found. The interaction between the shear force and Marangoni force played a solid state on the convection and heat transportation processes in the plasma arc welding process.